Diesel engines provide lower emissions and increased fuel economy compared to gasoline engines; however, if untreated diesel exhaust emissions are generally undesirable. Diesel particulate filters have been employed to control/treat particulate emissions from diesel-powered equipment such as trucks, buses, diesel electric locomotives and generators. Diesel particulate filters control diesel particulate emissions by physically trapping soot particles in their structure.
A typical diesel particulate filter body may be fabricated using, for example, a honeycomb structure having a matrix of intersecting thin, porous walls that extend across and between its two opposing open end faces and form a large number of adjoining hollow passages, or cells, which also extend between and are open at the end faces. To form a filter, one end of each of the cells is closed, preferably a first subset of cells being closed at one end face, and the remaining cells at the remaining end face. A contaminated fluid is brought under pressure to one face (the “inlet face”) and enters the filter body via the cells that are open at the inlet face (the “inlet cells”). Because the inlet cells are sealed at the remaining end face (the “outlet face”) of the body, the contaminated fluid is forced through the thin, porous walls into adjoining cells that are sealed at the inlet face and open at the opposing outlet face of the filter body (the “outlet cells”). The solid particulate contaminant in the fluid (such as soot), which is too large to pass through the porous openings in the walls, is left behind and a cleansed fluid exits the outlet face of the filter body through the outlet cells.
Such diesel filters are typically formed by an extrude-to-shape process, with many possible peripheral shapes or contours, for example, round, oval, and the like. However, when such shapes are employed, a problem arises in that it is nearly always the case that an integral number of complete cells do not fit into the cross-sectional area of the diesel filter. Thus, partial cells occur at the outer periphery of the diesel filter. These partial cells are located at the outermost periphery of the filter and, generally, the cell dimensions of these partial cells are smaller than the design value. Moreover, such cells generally are grouped in a line at various locations around the filter's periphery. Generally, automated plugging equipment used to plug alternating cells in diesel filters have difficulty in finding and plugging these peripheral partial cells, so that unplugged partial cells at the periphery may exist. Because these partial cells are unplugged, in operation unfiltered exhaust gas containing both particulate matter and NOx emissions may flow through them freely. Accordingly, a method of plugging these partial cells at the periphery of diesel filters is desired. Likewise, honeycomb filters, such as diesel filters, with a reduced number of unplugged partial cells around their periphery are much sought after.